This invention relates to emissions control systems for internal combustion engines in general and more specifically to systems for removing particulate matter from the exhaust gases produced by diesel engines.
One problem associated with the use of internal combustion engines, such as gasoline engines and diesel engines, arises from the formation of particulate matter during the combustion process. As is well-known, the presence in the exhaust gases of such particulate matter contributes to the undesirable emissions produced by such engines. Generally speaking, the solid particulate matter (i.e., soot) in diesel engine exhaust comprises small, solid, irregularly shaped particles, which are themselves agglomerates of smaller particles. The solid particulate matter may often have high molecular weight hydrocarbons absorbed on their surfaces. Frequently, the particulate matter is a complex mixture of pure carbon and various kinds of organic materials, and the sizes may range from very small particles of about 0.01 microns to relatively large clusters having sizes in the range of 10-30 microns, giving the particulate an extremely fine and light, flour-like consistency. Turbo-supercharged diesel engines tend to emit more of the smaller particles with much lower levels of retained organic compounds. However, regardless of the composition of the particulate matter, it tends to impose significant difficulties on the successful use of diesel engines in certain environments and for certain applications.
Many different types of exhaust treatment systems have been developed in an attempt to remove or eliminate the particulate matter before it is released into the atmosphere. Such systems almost always use some type of filter to trap the particles in the exhaust stream. Ceramic materials, stainless steel wire mesh, and other filter materials capable of withstanding the high-temperature exhaust gases have been tried and are being used with some degree of success. Unfortunately, because of the large quantities of particulate matter that are generated by most diesel engines, most filters tend to clog quickly, which increases back pressure in the engine exhaust and adversely affects the performance and efficiency of the engine. Of course, one remedy is to replace the filter when the back pressure exceeds some predetermined limit. However, the metal or ceramic filter materials used in most exhaust filters are expensive, so it is not practical to throw away the filters when they become clogged. As a result, several filter regeneration methods have been developed in attempts to solve the clogging problem. Unfortunately, the space, cost, and energy consumption required by such regeneration methods are substantial. Furthermore, in-situ filter regeneration techniques, where the filters rely on the hot exhaust gases themselves to raise the temperature of the filter to a level sufficient to oxidize the trapped particles, cannot be used with engines that operate under light duty-cycles.
Another type of exhaust treatment system, described in U.S. Pat. No. 5,272,874 entitled xe2x80x9cExhaust Treatment System,xe2x80x9d which is incorporated herein by reference for all that it discloses, represents a significant breakthrough in exhaust filtration technology. The system described in that patent utilizes a water cooled heat exchanger to lower the temperature of the exhaust gases, thereby allowing an inexpensive, low-temperature filter material to be used to trap exhaust-borne particles.
While the low-temperature particulate filter described in the foregoing patent is effective in removing the particulate matter with a high collection efficiency, it is not without its drawbacks. For example, the water cooled heat exchanger required to cool the exhaust gases represents an additional component which tends to add to the overall size, weight, and cost of the engine system, which can be a factor in certain applications.
Consequently, there remains a need for an improved exhaust gas filtration system that can effectively remove particulate matter from exhaust gases. Ideally, such a system should be capable of utilizing a low-temperature disposable particulate filter, which affords significant advantages, but without requiring a water cooled heat exchanger or other such device to lower the temperature of the exhaust gases to the point where such a low temperature filter may be used.
An induction cooled exhaust filtration system for filtering exhaust gases produced by an internal combustion engine may comprise a fan having an intake side and a discharge side and an ambient air inlet operatively associated with the intake side of the fan. A filter having an inlet surface and an outlet surface is positioned adjacent the fan so that the inlet surface of the filter is positioned adjacent the discharge side of the fan. An influx tube connected to the internal combustion engine is positioned so that its outlet end is located adjacent the intake side of the fan, so that the fan draws in air from the ambient air inlet and exhaust gases from the outlet end of the influx tube and discharges a mixture of air and exhaust gases from the discharge side and into the inlet surface of the filter.
Also disclosed is a method for filtering exhaust gases that comprises the steps of: Mixing the exhaust gases with ambient air to produce diluted exhaust gases; passing the diluted exhaust gases through a filter so that the filter removes particulate matter contained within the diluted exhaust gases; and discharging the filtered diluted exhaust gases into the atmosphere.